Optical beam control based on flexure actuation with positioning sensing and servo control

ABSTRACT

Implementations of actuators that use flexures to provide support to actuators and pivoting mechanisms to the actuators. Such actuators can be electromagnetically activated actuators that include a magnet stator and a coil rotor mounted on a flexure. A positioning sensor, such as a capacitor sensor, is provided to measure and monitor positioning of the actuator and is coupled to a feedback circuit which uses the measured positioning of the actuator to control the actuator.

PRIORITY CLAIM AND RELATED PATENT APPLICATION

This patent document claims the priority of U.S. Provisional ApplicationNo. 61/437,578 entitled “OPTICAL BEAM CONTROL BASED ON FLEXURE ACTUATIONWITH POSITIONING SENSING AND SERVO CONTROL” and filed Jan. 28, 2011 byBruce Borchers and Robert Stark, which is incorporated by reference aspart of the disclosure of this document.

BACKGROUND

This patent document relates to actuators and applications of suchactuators, including uses of such actuators in optical beam steering andscanning devices and systems.

An actuator is a device that can be activated by energy to cause motionor movement of a component attached or coupled to the actuator.Electromagnetically activated actuators can be configured to use acurrent-carrying coil in a magnetic field to electromagnetically causerotation of the coil by controlling the direction and amplitude of thecurrent in the coil. Bearing based galvonometers are examples of suchelectromagnetically activated actuators with coils.

SUMMARY

This document provides exemplary implementations of actuators that useflexures to provide support to the actuators and pivoting mechanisms tothe actuators. Such actuators can be electromagnetically activatedactuators that include a magnet stator and a coil rotor mounted on aflexure. The flexure can be designed, in some implementations, toeliminate the need for support bearings that tend to suffer frommechanical wear or fatigue after repetitive uses, to provide repeatablepositioning operations with reduced mechanical wear and fatigue. Theflexure, and to achieve a high positioning accuracy at a fast responsespeed. The power consumption of such flexure actuators can also besignificantly reduced or minimized in some implementations. Examples ofapplications of such actuators in optical steering and scanning areprovided.

For example, a flexure actuator device is provided to include a supportbase, a first flexure including a first flexure base that is fixed tothe support base and first flexure extensions that flex with respect tothe fixed first flexure base and the support base, and a second flexureincluding a second flexure base that is fixed to the support base andone or more second flexure extensions that flex with respect to thefixed second flexure base and the support base. The second flexure ispositioned and oriented to have the first and second flexure extensionsto cross. This device also includes an actuator engaged to distal endsof the first and second flexure extensions to rotate around a singlerotation axis as the first and second flexure extensions deform when theactuator is actuated to rotate. The actuator may be, for example, aconductor coil engaged to distal ends of the first and second flexureextensions and to rotate around the single rotation axis when anelectrical current in the conductor coil electromagnetically interactswith a magnetic field present at the conductor coil.

For another example, a method for operating a flexure actuator device todirect light is provided to include directing an input laser beam to amirror engaged to a flexure actuator device. This device includes asupport base, first and second flexures, and a conductor coil engaged tothe mirror to rotate with the conductor coil. The first flexure includesa first flexure base that is fixed to the support base and first flexureextensions that flex with respect to the fixed first flexure base andthe support base. The second flexure includes a second flexure base thatis fixed to the support base and second flexure extensions that flexwith respect to the fixed second flexure base and the support base. Theconductor coil is engaged to distal ends of the first and second flexureextensions to rotate around a single rotation axis as the first andsecond flexure extensions deform when an electrical current in theconductor coil electromagnetically interacts with a magnetic fieldpresent at the conductor coil. In this method, the electrical current iscontrolled to be at different current values to set the mirror atrespective different orientations to reflect the input laser beam alongdifferent directions set by the different orientations of the mirror.

For another example, a display device is provided to include a lightsource to produce one or more laser beams that are modulated to carryimages to be displayed, and a beam scanning module that scans the one ormore laser beams along two different directions on a screen surface todisplay the images and includes a first scanner to scan the one or morelaser beams along a first direction and a second scanner to scant theone or more laser beams along a second, different direction. The firstscanner includes a mirror and a flexure actuator device that engages themirror to rotate the mirror for scanning the one or more laser beamsalong the first direction. The flexure actuator device includes asupport base, first and second flexures, a conductor coil engaged to themirror to rotate the mirror. The first flexure includes a first flexurebase that is fixed to the support base and first flexure extensions thatflex with respect to the fixed first flexure base and the support base.The second flexure includes a second flexure base that is fixed to thesupport base and second flexure extensions that flex with respect to thefixed second flexure base and the support base. The conductor coil isengaged to distal ends of the first and second flexure extensions torotate around a single rotation axis as the first and second flexureextensions deform when an electrical current in the conductor coilelectromagnetically interacts with a magnetic field present at theconductor coil.

For another example, an actuator device includes a conductor coilelectrically connected to receive and carry an electrical current whichelectromagnetically interacts with a magnetic field present at theconductor coil to move the conductor coil, a coil support that isengaged to the conductor coil to confine movement of the conductor coilas a rotation around a rotation axis, a first Halbach magnet array offirst permanent magnets located at a first side of the coil support toproduce a first high magnetic flux density at a first side of theconductor coil, and a second Halbach magnet array of second permanentmagnets located at a second, opposite side of the coil support toproduce a second high magnetic flux density at a second side of theconductor coil. The first and second Halbach magnet arrays operatecollectively to rotate the conductor coil around the rotation axis. Thecoil support may include, in one example, two flexures that are crossedwith each other and are engaged to the conductor coil to confine themovement of the conductor coil to rotate around a location where the twoflexures are crossed.

For another example, a method for operating an actuator is provided toinclude engaging an actuator to a support base by first and secondflexures fixed to the support base. The first flexure includes a firstflexure base that is fixed to the support base and first flexureextensions that flex with respect to the fixed first flexure base andthe support base, and the second flexure includes a second flexure basethat is fixed to the support base and one or more second flexureextensions that flex with respect to the fixed second flexure base andthe support base. The second flexure is positioned and oriented to havethe first and second flexure extensions to cross, and the actuator isengaged to distal ends of the first and second flexure extensions torotate around a single rotation axis as the first and second flexureextensions deform when the actuator is actuated to rotate. This methodalso includes electrically coupling the actuator being to the firstflexure extension to receive an electrical actuator drive signal throughthe first flexure extension to cause the actuator to rotate and tomaintain at a position; providing a conductive sensing plate that isfixed in position relative to the actuator and to move with theactuator; providing a capacitor sensing device, that is fixed inposition relative to the support base and includes two electricallyconductive plates separated from each other to form a gap, to insertpart of the conductive sensing plate into the gap; using a thirdflexure, that includes a third flexure base that is fixed to the supportbase and a third flexure extension connected to the third flexure baseat one end and connected to the conductive sensing plate on the otherend, to form an electrically conductive path that is electricallyisolated from the first flexure and the electrical actuator drive signaltherein; and applying an electrical sensor signal which is conducted tothe conductive sensing plate. This method uses first and secondelectrical signals from the electrically conductive plates to produce aposition signal indicating a relative position of the conductive sensingplate relative one of the electrically conductive plates, and operates aservo control circuit coupled to the position sensing circuit and theactuator to produce a servo control signal based on the position signaland to control the actuator based on the position signal.

For yet another example, an actuator device is provided to include asupport base; a first flexure including a first flexure base that isfixed to the support base and first flexure extensions that flex withrespect to the fixed first flexure base and the support base; and asecond flexure including a second flexure base that is fixed to thesupport base and one or more second flexure extensions that flex withrespect to the fixed second flexure base and the support base. Thesecond flexure is positioned and oriented to have the first and secondflexure extensions to cross. In this device, an actuator is engaged todistal ends of the first and second flexure extensions to rotate arounda single rotation axis as the first and second flexure extensions deformwhen the actuator is actuated to rotate and the actuator is electricallycoupled to the first flexure extension to receive an electrical actuatordrive signal through the first flexure extension to cause the actuatorto rotate and to maintain at a position. A platform is fixed to theactuator and to move with the actuator, and includes a first sidegrating facet that has electrically conductive first grating teeth thatare electrically connected to one another. A side grating module isfixed to the support base and separated from the platform and theactuator so that platform and the actuator move relative to the sidegrating module. This side grating module includes a second side gratingfacet that has electrically conductive second grating teeth that areelectrically connected to one another and positioned adjacent to thefirst grating teeth and separated from the first grating teeth by a gap.This device includes a position sensing circuit coupled to the firstgrating teeth and the second grating teeth to apply an electrical sensorsignal and a servo control circuit coupled to the position sensingcircuit and the actuator. The position sensing circuit includes aprocessing circuit that receives first and second electrical signalsfrom the first and second grating teeth, respectively, and produces aposition signal from the received first and second electrical signalsindicating a relative position of the platform relative to the sidegrating module. The servo control circuit is operable to produce a servocontrol signal based on the position signal and operable to control theactuator based on the position signal.

These and other examples, implementations and applications ofelectromagnetically activated actuators based on flexures are describedin detail in the drawings, the detailed description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show two views of an example of an electromagneticallyactivated actuator with a magnet stator and a coil rotor mounted on aflexure.

FIG. 3 shows operations of the magnet module and the conductor coil inthe actuator in FIGS. 1 and 2.

FIGS. 4A and 4B show an implementation of the electromagneticallyactivated actuator in FIGS. 1 and 2.

FIGS. 5A and 5B illustrate an example of an actuator feedback controlfor an actuator-mirror assembly based on the designs in FIGS. 1-4B.

FIG. 6 shows an operation of the electromagnetically activated actuatorin FIGS. 1 and 2.

FIGS. 7A, 7B and 7C show examples of scanning display systems using anelectromagnetically activated actuator.

FIGS. 8A, 8B and 8C show examples of scanning laser display systemhaving a light-emitting screen made of laser-excitable light-emittingmaterials with feedback from the screen for beam alignment feedbackcontrol.

FIGS. 9A, 9B, 10, 11A, 11B and 12 show examples of display systems andoperations based on the system in FIGS. 8A and 8B.

FIGS. 13A through 22 show various implementations of capacitor positionsensor based flexure actuator.

FIGS. 23A, 23B and 23C illustrate an example of a charged gratingcapacitor sensing design for measuring and controlling the positioningof the mirror platform supported by the flexure actuator.

DETAILED DESCRIPTION

FIGS. 1 and 2 show two views of an example of an electromagneticallyactivated actuator device with a magnet stator and a coil rotor mountedon a flexure. The flexure is designed to provide support to the actuatorand a pivoting mechanism to the actuator. The electromagneticallyactivated actuator based on a coil is an example of various actuatordesigns and other actuator designs can also be used with the presentflexure design.

The illustrated actuator deice includes a support base 101, a conductorcoil 120 as a rotor, and a flexure 110 that connects to the coil 120 andthe support base 101 to movably suspend the conductor coil 120 relativeto the support base 101. A magnet module 140, which may include twoHalbach magnet arrays, is fixed in position relative to the support base101 to produce a magnetic field with a desired spatial fielddistribution pattern at the conductor coil 120 to electromagneticallycause the conductor coil 120 to rotate, in response to an electricalcurrent that is supplied to the conductor coil 120, around a singlerotation axis defined by the flexure 110 and the manner that the flexure110 is engaged to the support base 101. The magnet module 140 has agroove 190 with magnetic materials as walls in which a side of the coil120 is placed to be exposed to a high magnetic flux area inside thegroove 190. In some implementations, the groove 190 is designed to besufficiently large so that the side of the coil 120 in the groove 190remains substantially inside the groove 190 at different orientations ofthe coil 120.

In this example, the support base 101 and the magnetic module 140 areseparate components and are fixed in position relative to each other. Inother implementations, the magnetic module 140 may be structured toproduce the desired magnetic field at the coil 120 and to engage to theflexure 110 as a support base. The flexure 110 includes two differentflexure parts in a cross configuration to provide the desired mechanicalsuspension of the conductor coil 120 and the desired constraint to themovement of the conductor coil 120 so that the conductor coil 120rotates around the single rotation axis. In FIG. 1, the single rotationaxis is perpendicular to the paper as marked by the arrowed lineindicating the rotation. This flexure based design can be used toeliminate mechanical bearings, minimize rotational inertia, and canprovide accurate positioning of the conductor coil 120 and a fastresponse speed.

Referring to FIG. 1, the magnet module 140 is designed to produce adense magnetic flux density at the location of the conductor coil 120and the electromagnetic interaction of the current flowing inside theconductor coil 120 and the magnetic field of the magnet module 140causes the conductor coil 120 to rotate. The current is controlled tochange its magnitude and thus to control the rotation and/or position ofthe conductor coil 120. The direction of the rotation of the conductorcoil 120 is controlled by changing the direction of the current insidethe conductor coil 120.

A control circuit is provided to supply and control the direction andmagnitude of the current to the conductor coil 120. The control circuitcan control the current to cause various modes of movement or motion atthe conductor coil 120. The current can be set in various currentvariation patterns to cause various rotation patterns at the conductorcoil 120: a continuous rotation over an angular range, a periodic backand forth oscillation within an angular range, discrete positions, andothers. For example, such a flexure actuator can be used to control amirror that is engaged to the conductor coil 120 for controlling anoptical beam reflected by the mirror in some applications including thescanning beam systems described herein. In one mode of operation of sucha scanning beam system, the flexure actuator can be controlled to setthe mirror at two or more discrete orientations where each discreteorientation is controlled with a desired orientation accuracy. Inoperation, the control circuit sets a pre-set current at a givenmagnitude and direction to cause the conductor coil 120 to rotate to aparticular angle and stay there until the current is changed. Asdescribed below, a positioning sensor can be provided to monitor theactual positioning of the conductor coil 120 and the current set at aparticular magnitude can be adjusted based on the monitored positioninginformation in a feedback control configuration to ensure that thepositioning or rotation angle of the conductor coil 120 is maintained atthe desired angle within a permissible tolerance range.

In one implementation of the flexure actuator, the magnet module 140 caninclude two permanent magnet modules placed on two sides of the supportbase 101. As an example, multiple magnets may be used to form a Halbacharray 210 in FIG. 2 for each of the two modules 140 to produce asufficiently high or dense magnetic flux density at the coil 120. Thetwo Halbach arrays 210 are structured to have opposite polarity in theirmagnetic fields. Therefore, with the current flowing in one directioninside the coil 120, one of the two magnet modules 210 has a magneticattraction to the coil induced field while the other magnet module 210is set to repel the coil induced field. The result is the teeter-tottereffect to efficiently generate a force and a torque on the conductorcoil 120 to move the conductor coil 120.

FIG. 3 shows an example of using two Halbach arrays 210 in FIG. 2. EachHalbach array 210 is formed by five permanent magnets 211, 212, 213, 214and 215. The magnetic polarities (indicated by “N” and “S”) of the givepermanent magnets 211, 212, 213, 214 and 215 are arranged as shown toproduce desired high magnetic flux densities at the two parallel sidesof the coil 120 to exerting a torque on the coil 120 to rotate. EachHalbach array 210 includes three magnets 211, 212 and 213 on the bottomand two top magnets 214 and 215 that are positioned on top of the bottommagnets 211, 212 and 213. The two top magnetic 214 and 215 are spacedfrom each other to form the groove 190 which is a cavity indentsurrounded by permanent magnets 214, 215 and 213. The spatialdistribution of the magnetic flux is illustrated, showing the highestflux density inside the groove 190 where a respective side of the coil210 is located. In some implementations, the dimensions of the magnets214 and 215 and the spacing between the magnets 214 and 215 are set torender the groove 190 to be sufficiently large so that the side of thecoil 120 in the groove 190 remains substantially inside the groove 190at different orientations of the coil 120. The sizes, dimensions andlocations of the five permanent magnets are designed with respect to oneanother to produce a strong magnetic field flux density at two oppositesides of the coil 120 to change the orientation of the coil 120 at ahigh speed. This design of using two Halbach arrays with a conductorcoil to form an electromagnetic actuator is advantageous than variousother galvonometer designs because the two Halbach arrays are configuredto provide efficient electromagnetic interactions between the magnetsand the coil. Other designs may also be used.

In FIGS. 1 and 2, a damper 150 is provided between the support base 101and the conductor coil 120 to dampen a motion of the conductor coil 120relative to the support base 101. Two such dampers 150 may be providedon two opposite sides of the conductor coil 120 to provide symmetricdamping.

Such an actuator in FIGS. 1 and 2 can be used in various applications.As an example, FIGS. 1 and 2 show a mirror 130 engaged to the conductorcoil 120 so that the mirror 130 rotates with the conductor coil 120around the single rotation axis. This actuated mirror device can be usedto steer or scan an optical beam in, e.g., a beam scanning device suchas scanning a laser beam in a scanning beam display system described inthis document. As shown in FIG. 1, an input beam 181 is directed ontothe mirror 130 and is reflected by the mirror 130 as an output beam 182along a desired output direction dictated by the orientation of themirror 130. When the input beam 181 is at a fixed input direction to themirror 130, the rotation of the mirror 130 changes the output directionof the output beam 182.

FIGS. 4A and 4B show an exemplary implementation of the actuator shownin FIGS. 1 and 2. FIG. 4A shows the assembled actuator and FIG. 4B is anexploited view of the actuator to show various components or parts ofthe actuator.

In this example, the flexure 110 in FIGS. 1 and 2 is implemented as atwo-part flexure assembly: a first flexure 410 and a second flexure 420.This two-part flexure assembly is engaged to a support base 430 as anexample of the support base 101 in FIGS. 1 and 2. The first flexure 410includes a first flexure base 411 that is fixed to the support base 430and two first parallel flexure extensions 413 and 414 that flex withrespect to the first flexure base 411 and the support base 430. Thefirst flexure base 411 in this example is elongated along the singlerotation axis 490 of the conductor coil 120 to provide rigidity againstany motion of the first flexure 410 in a direction different from thesingle rotation axis. The two first parallel flexure extensions 413 and414 are elongated along a direction that is perpendicular to the singlerotation axis conductor coil 120 to flex around the first flexure base411.

Similarly, the second flexure 420 includes a second flexure base 421that is fixed to the support base 430 and two second parallel flexureextensions 423 and 424 that flex with respect to the second flexure base421 and the support base 430. The second flexure base 421 in thisexample is elongated along the single rotation axis of the conductorcoil 120 to provide rigidity against any motion of the second flexure420 in a direction different from the single rotation axis. The twosecond parallel flexure extensions 423 and 424 are elongated along adirection that is perpendicular to the single rotation axis conductorcoil 120 to flex around the second flexure base 421. Alternatively, thesecond flexure 420 may include the second flexure base and one flexureextension that flexes with respect to the second flexure base 421, ormay include three or more flexure extensions.

The first and the second flexures 410 and 420 are positioned andoriented to have the first flexure extensions 413 and 414 to spatiallycross with the second flexure extensions 423 and 424 so that theactuator engaged to the distal ends of the first and second flexureextensions rotate or pivot approximately around the location of thecross. In the illustrated example, the first and the second flexures 410and 420 are positioned and oriented to have the first flexure extensions413 and 414 to spatially interleave with the second flexure extensions423 and 424 in position along a direction parallel to the direction ofthe single rotation axis. Under the cross configuration, the conductorcoil 120 is engaged to distal ends of the first and second flexureextensions 413, 414, 423 and 424 to rotate around the single rotationaxis as the first flexure extensions 413 and 414 counter act to thesecond flexure extensions 423 and 424 and vice versa when the conductorcoil 120 is in motion. When viewed along the single rotation axis, thefirst flexure extensions 413 and 414 and the second flexure extensions423 and 424 cross one another as shown in FIG. 1. As illustrated, thedistal ends of the first flexure extensions 413 and 414 that are engagedto the conductor coil 120 are located above the second flexure base 421,and the distal ends of the second flexure extensions 423 and 424 thatare engaged to the conductor coil 120 are located above the firstflexure base 411. Therefore, the crossed flexures 410 and 420 provide abearing-free pivoting mechanism by crossing two flexures 410 and 420 ofequal lengths for the flexure extensions 413, 414, 423 and 424 andhaving one side of the cross flexures to be attached to the stationarybase 430 and the other sides to be joined onto the free floatingplatform of the conductor coil 120. In operation, if the conductor coil120 is tilted by the electromagnetic interaction between the current inthe coil and the magnetic field, one side of the conductor coil 120 ispulled down as the other side is pushed up so that the pulled-down sideof the conductor coil 120 causes one flexure side to bend down whilecausing the other flexure side to be up. The mutual pressures constrainthe rotational tilt motion of the conductor coil 120 and the frictionassociated with the rotation of the coil 120 is negligibly small becausethe flexure design is free of a friction between two components movingrelative to each other as the conductor coil 120 rotates. This aspectallows the device to consume low power and a minimal counter-force issufficient to maintain the tilt of the conductor coil 120 when holdingthe conductor coil 120 at a fixed position. To reduce the overall massto be moved by the actuator, the coil 120 can be directly attached tothe mirror 130. To further reduce added materials and the mass of theactuator, the flexures 410 and 420 are electrically connected to thecoil 120 for directing the current flow to and from a current generatorthat supplies the current to the coil 120.

The crossed flexures 410 and 420 in FIGS. 4A and 4B are designed toallow the coil-mirror assembly to rotate around one axis. The remainingfive degrees of freedom of motion are constrained by the flexuregeometry. The off axis stiffness of the flexures 410 and 420 can bedesigned to be much higher than the stiffness around the single rotationaxis, e.g., about 1,000 times greater than the on axis stiffness. Thiscan be achieved by designing the shape of the flexure bases 411 and 421,the engagement of the flexure bases 411 and 421 to the support base, andthe widths of the flexure extensions 413, 414, 423 and 424 to achieve adesired aspect ratio of the flexure cross section and thus the largedifference between the off-axis stiffness and the on-axis stiffness. Theflexure design can be configured to keep the parasitic resonance at highfrequencies, e.g., greater than 12 KHz.

This flexure actuator design can be used to achieve one or moreadvantages in implementations. For example, this flexure actuator designcan be used to eliminate a motor shaft, moving magnets, and bearingassemblies to reduce friction in the actuator operation and therotational inertia of the actuator. For another example, the crossflexure can be structured to mitigate mechanical wear in bearing orbushing used in some other actuator designs. By minimizing stress in theflexures during deflection, the cross flexure design can be configuredto operate at low actuation/holding torques, to have a high parasiticresonance, a low rotational inertia, a low flexure stresses whendeflected and to keep the stress below the endurance limit of theflexure material for a practically near infinite operating life. Inaddition, the cross flexures can be used as coil leads to conduct theelectrical current to the coil 120 to minimize or avoid use of flexibleleads that are used for conducting the current for coils in otherdesigns. This use of the cross flexures as coil leads can furtherenhance the reliability of the actuator device because flexible leadsare subject to mechanical fatigue due to movement of the flexible leadswith the coil and the fatigue can lead to breakage of the flexibleleads.

The support base 430 shown in FIG. 4A includes several components asshown in FIG. 4B. The support base 430 has two support base parts 431and 432 that are engaged to each other by a fastener 433, e.g., a caphead screw. The flexure bases 411 and 421 are engaged to the supportbase part 431 in this example. Referring to FIG. 4A, the support base430 includes two protruded extensions 434 and 435 on the opposite sidesof the conductor coil 120 and the mirror 130. A first damper is locatedbetween and in contact with the protruded extension 434 and the firstside surface of the coil 120 or the mirror 130 to dampen a motion of theconductor coil 120 relative to the support base 430. A second damper islocated between and in contact with the protruded extension 435 and theside surface of the coil 120 or the mirror 130 to dampen the motion ofthe conductor coil 120 relative to the support base 430. Such dampersare represented by the part 150 in FIGS. 1 and 2 and can be made from agel, a silicone damping material, or other suitable materials.

The flexure based actuator in FIGS. 4A and 4B can be designed to quicklyand accurately move from one position to another position in atilt-rotated manner. The flexure design allows a stationary and stablepositional state and provides minimal power consumption to maintain thestationary stable positional state. This actuator can perform repeatablerotation operations without degradation of the performance. For example,a fast operation time less than 100 μs can be achieved in transitioningthe actuator between either of two pre-determined mirror positions. Thecross flexure design can be used to achieve a small angular rotation(e.g., 0.06 degrees) and a fine angular resolution, e.g., 0.0006 degreesor about 10 μrad. The average power consumption of the actuator can below, e.g., 0.6 watts. A relatively large payload can be used with thisdesign, e.g., a 9 mm×9 mm mirror that weights about 0.2 grams. Theconductor coil 120 may have multiple conductor windings (e.g., 15 turns)to provide sufficient torque due the electromagnetic interaction betweenthe coil 120 and the magnetic field of the magnetic module 140. In someimplementations, the mirror 130 can be maintained at a steady stateposition to better than 0.00006 degrees or about 1 μrad, whilemaintaining an average hold current of less than 50 mA plus or minusperturbations caused by the feedback mechanism as described below. Thelifetime for such a flexure can be practically infinite and the life ofthe actuator using such a flexure may depend on the life of theengagement mechanism for the flexure, such as the adhesive used, andother components such as the laser diode used for optical monitoring ofthe flexure-mirror assembly for a feedback control described below. Along lifecycle of more than 10¹³ cycles for such an actuator should beachievable.

FIG. 4B further shows that the permanent magnet 125 of the Halbach array210 that is located inside the loop of the coil 120 has a cut outfeature 490 at each of the two opposite ends of the magnet 150. Thesecut out features 490 are provided to further enhance the magnetic fluxdensity inside the groove 190 to provide high-speed switching operationsof the coil 120.

In some applications, the flexure-based actuator may include a feedbackcontrol mechanism that monitors the orientation of the actuator andprovides a feedback signal to stabilize the actuator position at adesired position against any fluctuations or drifts in the actuatorposition. FIGS. 5A and 5B illustrate an example of an actuator feedbackcontrol for an actuator-mirror assembly based on the designs in FIGS.1-4B.

Referring to FIG. 5A, the feedback control for a flexure-basedactuator-mirror assembly 510 includes a laser diode 521 that produces amonitoring laser beam 522 towards the mirror 130. A collimation lens 523may be used to collimate the laser beam 522. This monitoring laser beam522 is different from and is an addition to an optical beam to beredirected by the mirror 130. The monitoring laser beam 522 can be at awavelength different form the wavelength of the optical beam to beredirected by the mirror 130. For example, if the optical beam tore-directed by the mirror 130 is a visible beam, the monitoring laserbeam 522 may be an invisible beam, e.g., an IR beam. Upon reflection bythe mirror 130, the reflected beam 524 is directed into a positionsensitive detector (PSD) 530 that is located at a fixed known locationwith respect to the flexure-based actuator-mirror assembly 510. Thepositions of the laser diode 521 and PSD 530 are fixed relative to theflexure-based actuator-mirror assembly 510 so that each position of thebeam 524 on the sensing surface of the PSD 530 corresponds to aparticular orientation of the mirror 130. As such, the position of thebeam 524 on the PSD 530 can be used to measure the orientation of themirror 130. Therefore, if the orientation of the mirror 130 deviatesfrom a desired orientation, the actual beam position of the beam 524 onthe PSD 530 deviates from a desired beam position on the PSD 530. Thisdifference in position on PSD 530 can be used as an error signal toadjust the mirror 130 to reduce the error.

In FIG. 5A, the feedback control includes an actuator control module 550that receives the PSD output 532 from the PSD 530. The control module550 compares the beam position on the PSD 530 in the received PSD output532 to a desired beam position on the PSD 530 and determines an error inthe PSD position for the beam 524. Based on this error, the controlmodule 550 generates a control signal 552 to a current generator 560that supplies the electric current 562 to the conductor coil 120 toadjust the orientation of the conductor coil 120 and thus theorientation of the mirror 130 to reduce the error. As illustrated, aninput beam 181 is directed onto the mirror 130 and is redirected by themirror 130 as an output beam 182. The beams 522 and 524 which are usedfor monitoring the orientation of the mirror 130 so that the input beam181 can be redirected as the output beam 182 at a desired outputdirection at a given moment.

Turning to FIG. 5B, a support frame 501 is provided to hold the PSD 530,the laser diode 521, the flexure-based actuator-mirror assembly 510 infixed positions relative to one another. An optical sensor filter 540may be inserted in front of the PSD 530 to filter the light so that onlythe light of the feedback monitoring laser beam 524 is received by thePSD 530 while other light, such as light from the beams 181 and 182shown in FIG. 5A, is rejected by the filter 540. The laser diode 521 andthe collimation lens 523 can be included in a laser diode-lens assembly520 mounted on the support frame 501. An extension mirror 570 on thesupport frame 501 can be used to guide light of the beams 522 and 524between the flexure-based actuator-mirror assembly 510 and the PSD 530and the laser diode-lens assembly 520. This extension mirror 570 may beused to increase the optical path length from the laser diode-lensassembly 520 to the assembly 510 and to the PSD 530 to increase thechange of the beam position of the feedback monitoring laser beam 524 onthe PSD 530 with respect to a change in the tilt of the mirror 130 inthe assembly 510.

In operating the flexure actuator described in this document, theelectrical current supplied to the conductor coil 120 can be controlled,prior to setting the electrical current to a desired fixed value forachieving a desired mirror orientation, to reverse the direction of theelectrical current from a desired direction of the electrical currentfor achieving the desired mirror orientation. This operation can be usedto reduce over shoot of the mirror 130 beyond the desired mirrororientation. FIG. 6 illustrates an example of this current controloperation for setting the mirror 130 in two orientations. Referring backto FIG. 5A, when the flexure is in a first position, the feedbackmonitoring laser beam 524 is to be at a beam position on the PSD 530 ofthe first pre-identified target point and when the flexure is in thesecond position, the feedback monitoring laser beam 524 is to be at asecond beam position on the PSD 530 corresponding to the secondpre-identified target point. Any offset form either point is used in thefeedback loop to the current driven through the coil windings creatingoffset positioning of the steady state position of the mirror.

In the example shown in FIG. 6, the nominal steady state current throughthe winding is nearly 50 mA. If one of the target positions is near thepower off position of the flexure module, then the steady state currentmay be less. By integrating the actuator and sensor into a rigidassembly ultra stable angular measurement can be achieved. For example,the flexure assembly can be designed with a first parasitic resonance at12 Khz, but the current through the windings is set at a transitionspeed of 4 Khz below the first parasitic resonance, so from the firstmirror position to the second mirror position current flows in onedirection through the windings up to 1 A for 60 usec to accelerate therotation of the mirror to the second position, followed immediately by atransition to a second reverse current through the windings of again upto 1 A, then the current is altered to achieve the steady state positionfor the mirror which may be nearly 50 mA based on the final position ofthe mirror. The maximum current applied to accelerate the mirror andthen decelerate the mirror is based on position of the mirror in termsof the expected stress of the flexures. The current first and secondpolarity is based on the direction of the rotation in relation to thewinding orientation in the coil to the two magnets. Mechanical and/orelectronic damping can be used to minimize first resonance ringing inthe actuator. In this implementation a gel is used on the edge of theplatform to help dampen movement and better retain a stable stationaryposition.

In FIG. 6, the switching period between the two mirror positions A and Bis 4.16 msec. The current through the coil winding is sent at time T1 inone polarity (e.g. positive) of a current approximately 0.5 A peak. Toslow the tilt motion of the mirror, the current is reduced beginning attime T2. To decelerate the tilt of the mirror, a reverse current isapplied at time T3 to a max reverse current at time T4, where thecurrent returns to a stable state at time T5. Here the current is at anormalized value to hold the mirror in place, where the current isapplied to create a electromagnetic force to counter the force of thebent-to-position flexure. This steady state current is modulated by thefeedback circuit to correct for any drift of the flexure-mirror platformor a variation in the input laser beam directed to the mirror. Thecurrent mostly normalizes to a steady state current of typically 50 mA.The reverse action takes place to tilt the mirror back from the positionA to position B. This process begins with a current in the oppositedirection of the steady current used for holding the coil at theposition A at time T6, reduces the magnitude of the applied currentafter reaching at a peak of 0.5 A at time T7, reverses the direction ofthe current at T8 to increase the current amplitude to a peak at T9, andthen reduces the magnitude to ultimately reach a steady state current attime T10 for holding the mirror at a steady state position B.

Among various applications that can implement the present flexure-basedactuator, the following examples describe scanning-beam systems forproducing optical patterns by using two beam scanners to scan one ormore optical beams in raster scanning patterns. Some laser printingsystems use a scanning laser beam to print on a printing surface of aprinting medium (e.g., paper). Some display systems use 2-dimensionallyscanned light to produce images on a screen.

FIGS. 7A, 7B and 7C show examples of scanning beam systems that use twoscanners: a polygon scanner with multiple reflective facets to providehorizontal scanning and a vertical scanning mirror such as agalvo-driven mirror to provide vertical scanning. A laser source 710 isprovided to produce at least one laser beam 712. Depending on thespecific applications, this single beam can be a beam of a particularwavelength, e.g., a visible color, UV light or other wavelengths. Insome applications, multiple beams 712 may be generated from the lasersource 710 and are scanned. In some implementations, the different beams712 may be of different wavelengths, e.g., red, green and blue colors inthe visible range, while in other implementations, the different beams712 may be of the same or similar wavelengths, e.g., UV light. Twoscanners, a polygon horizontal scanner 740 and a vertical scanner 750,are used to scan the beams 712 onto a surface 701 on a target device702, e.g., a screen. Notably, the vertical scanner 750 can beimplemented by using the present flexure-based actuator-mirror assembly.In operation, one facet of the polygon scanner 740 scans one horizontalline as the polygon scanner 740 spins to change the orientation andposition of the facet and the next facet scans the next horizontal line.The horizontal scanning and the vertical scanning are synchronized toeach other to project images on the screen 702. Such a two-scanneroptical scanning system can be in a pre-objective optical design asshown in FIG. 7A where a scan lens 760 is placed in the optical pathdownstream from the polygon scanner 740 and the vertical scanner 750 tofocus a scanning beam onto the target surface 701, e.g., a screen.Because the scan lens 760 is positioned downstream from the polygonscanner 740 and the vertical scanner 750, the beam entering the scanlens 760 is scanned along the vertical and horizontal directions.Therefore, the scan lens 760 is designed to focus the 2-dimensionallyscanned beam onto the target surface. In this example, the verticalscanner 750 is placed upstream from the polygon scanner 740.Alternatively, the order of the two scanners 740 and 750 may bereversed.

FIGS. 7B and 7C show two exemplary implementations of a post-objectivescanning system where a scan lens is placed in an optical path betweenthe two scanners. In the example in FIG. 7B, the first scanner is thepolygon scanner 740. The beam 712 is scanned along the first direction(e.g., the horizontal direction) by the polygon scanner 740 as a 1-Dscanning beam 714. The second scanner downstream from the polygonscanner 740 is the vertical scanner 750, e.g., a galvo mirrorconstructed by engaging a mirror to a galvanometer and operates to scanthe horizontally scanning beam 714 along the vertical direction as a 2-Dscanning beam 116 to a target surface 701. A scan lens 720 is placedbetween the two scanners 740 and 750. In this post-objective design, thescan lens 720 can be structured to have high optical performance infocusing the 1-D scanning beam 114 along the scanning direction of thefirst scanner 140 only. Hence, such a scan lens does need to exhibithigh optical performance along the second scanning direction (i.e., thevertical direction in this example) because the beam 714 is not scannedalong the second scanning direction at the position of the scan lens720. Therefore, the scan lens 720 can be a 1-D scan lens, e.g., a 1-D ftheta lens. Due to the design of the scan lens 720, the focusing of thebeam 116 on the target surface 701 does not change with the horizontalscanning. In addition, the vertical scanner 750 in FIG. 7B scans at amuch smaller rate as the second scanner than the scan rate of the firsthorizontal scanner 740 and thus a focusing variation caused by thevertical scanning on the target surface 701 varies with time at theslower vertical scanning rate. This allows a focusing adjustmentmechanism to be implemented in the system of FIG. 7B with the lowerlimit of a response speed at the slower vertical scanning rate ratherthan the high horizontal scanning rate. In practical devices, thisparticular arrangement of two scanners 740 and 750 allows easyimplementation of the dynamic focusing adjustment to maintain the properfocusing of the 2-D scanning beam on the target surface as the verticalscanner 750 scans along the vertical direction.

When multiple beams 712 are used, each facet of the polygon scanner 740simultaneously reflects the horizontal scan for a number of laser beamson the surface 701. The surface 701 is divided into a number of swathregions and each region corresponds to one polygon facet. In oneimplementation, multiple passes of the polygon scanner 740 can be usedfor the horizontal scanning with the beams at one vertical level for onepass and a slight vertical position offset for the next pass to achievea vertical resolution set by the vertical position offset. The verticalscanner 750 is used to generate this slight vertical position offset.Assuming the polygon scanner 740 rotates once every 4.16 msec, then thevertical scanner 750 tilts one direction or the opposite direction onceper revolution of the polygon scanner 740, e.g., once per 4.16 msec inthe example in FIG. 6.

FIG. 7C illustrates an example of a post-objective scanning system wherethe vertical scanner 750 is upstream to the polygon scanner 740. Thelaser beam 712 from the laser 710 is directed to the vertical scanner750 which scans the beam in the vertical direction as the 1-D scanningbeam 731 and directs the beam 731 through the scan lens 720 to thedownstream polygon canner 740. The output beam 732 from the polygonscanner 740 is a 2-D scanning beam and is directed to the target surface701. In one implementation, the scan lens 720 can be designed to imagethe reflective surface of the vertical scanner 750 onto the reflectingfacet of the polygon scanner 740 so that a relatively small polygonfacet of a compact polygon can be used to reduce power consumption andthe dynamic range of the polygon.

The scanning-beam systems described above can be configured as displaysystems with either a passive screen or active screen as the targetdevice 702. A passive screen does not emit light but makes light of theone or more scanning beams visible to a viewer by one or a combinationof mechanisms, such as optical reflection, optical diffusion, opticalscattering and optical diffraction. For example, a passive screen canreflect or scatter received scanning beam(s) to show images. An activescreen emits light by absorbing the one or more scanning beams and theemitted light forms part of or all of the light that forms the displayedimages. Such an active screen may include one or more fluorescentmaterials to emit light under optical excitation of the one or morescanning beams received by the screen to produce images. Screens withphosphor materials under excitation of one or more scanning excitationlaser beams are described here as specific implementation examples ofoptically excited fluorescent materials in various system.

FIG. 8A shows an example of a scanning beam display system that use afluorescent screens with fluorescent materials to emit light underoptical excitation to produce images. Various screen designs withfluorescent materials can be used. In one implementation, for example,three different color phosphors that are optically excitable by thelaser beam to respectively produce light in red, green, and blue colorssuitable for forming color images can be formed on the screen asrepetitive red, green and blue phosphor stripes in parallel. Variousexamples described in this application use screens with parallel colorphosphor stripes for emitting light in red, green, and blue toillustrate various features of the laser-based displays. Phosphormaterials are one type of fluorescent materials. Various describedsystems, devices and features in the examples that use phosphors as thefluorescent materials are applicable to displays with screens made ofother optically excitable, light-emitting, non-phosphor fluorescentmaterials. At least one scanning laser beam is used to excite colorlight-emitting materials deposited on a screen to produce color images.The scanning laser beam is modulated to carry images in red, green andblue colors or in other visible colors and is controlled in such a waythat the laser beam excites the color light-emitting materials in red,green and blue colors with images in red, green and blue colors,respectively. Hence, the scanning laser beam carries the images but doesnot directly produce the visible light seen by a viewer. Instead, thecolor light-emitting fluorescent materials on the screen absorb theenergy of the scanning laser beam and emit visible light in red, greenand blue or other colors to generate actual color images seen by theviewer. The excitation optical beam that excites a fluorescent materialon the screen can be at a frequency or in a spectral range that ishigher in frequency than the frequency of the emitted visible light bythe fluorescent material.

Accordingly, the excitation optical beam may be in the violet spectralrange and the ultra violet (UV) spectral range, e.g., wavelengths under420 nm.

In FIG. 8A, the laser-based display system uses a screen having colorphosphor stripes. Alternatively, color phosphor dots may also be used todefine the image pixels on the screen. The system includes a lasermodule 810 to produce and project at least one scanning laser beam 820onto a screen 801. The screen 801 has parallel color phosphor stripes inthe vertical direction where red phosphor absorbs the laser light toemit light in red, green phosphor absorbs the laser light to emit lightin green and blue phosphor absorbs the laser light to emit light inblue. Adjacent three color phosphor stripes are in three differentcolors. One particular spatial color sequence of the stripes is shown inFIG. 8A as red, green and blue. Other color sequences may also be used.The laser beam 820 is at the wavelength within the optical absorptionbandwidth of the color phosphors and is usually at a wavelength shorterthan the visible blue and the green and red colors for the color images.As an example, the color phosphors may be phosphors that absorb UV lightin the spectral range from about 380 nm to about 420 nm to producedesired red, green and blue light. The laser module 810 can include oneor more lasers such as UV diode lasers to produce the beam 820, a beamscanning mechanism to scan the beam 820 horizontally and vertically torender one image frame at a time on the screen 801, and a signalmodulation mechanism to modulate the beam 820 to carry the informationfor image channels for red, green and blue colors. Such display systemsmay be configured as rear scanner systems where the viewer and the lasermodule 110 are on the opposite sides of the screen 101. Alternatively,such display systems may be configured as front scanner systems wherethe viewer and laser module 110 are on the same side of the screen 801.

This scanning display system can be calibrated during the manufactureprocess so that the on and off timing of the optical pulses carried bythe scanning laser beam 820 and positions of the laser beam 820 relativeto the fluorescent stripes in the screen 801 are known and arecontrolled within a permissible tolerance margin in order for the systemto properly operate with specified image quality. However, the screen801 and components in the laser module 810 of the system can change overtime due to various factors, such as scanning device jitter, changes intemperature or humidity, changes in orientation of the system relativeto gravity, settling due to vibration, aging and others. Notably, suchchanges can produce visible and, often undesirable, effects on thedisplayed images. For example, a laser pulse in the scanning excitationbeam 820 may hit a subpixel that is adjacent to an intended targetsubpixel for that laser pulse due to a misalignment of the scanning beam820 relative to the screen 801 along the horizontal scanning direction.When this occurs, the coloring of the displayed image is changed fromthe intended coloring of the image. Hence, a red flag in the intendedimage may be displayed as a green flag on the screen. For anotherexample, a laser pulse in the scanning excitation beam 820 may hit boththe intended target subpixel and an adjacent subpixel next to theintended target subpixel due to a misalignment of the scanning beam 820relative to the screen along the horizontal scanning direction. Whenthis occurs, the coloring of the displayed image is changed from theintended coloring of the image and the image resolution deteriorates.The visible effects of these changes can increase as the screen displayresolution increases because a smaller pixel means a smaller tolerancefor a change in position. In addition, as the size of the screenincreases, the effect of a change that can affect the alignment can bemore pronounced because a large moment arm associated with a largescreen means that an angular error can lead to a large position error onthe screen. For example, if the laser beam position on the screen for aknown beam angle changes over time, the result is a color shift in theimage. This effect can be noticeable and thus undesirable to the viewer.

The system in FIG. 8A implements a feedback control mechanism tomaintain proper alignment of the scanning beam 820 on the desiredsub-pixel to achieve desired image quality. An optical sensing module830 is provided to receive feedback light that is emitted by the screen801 under optical excitation of the excitation beam 820 and representsthe position and other properties of the scanning beam 820 on the screen801. The optical sensing unit 830 produces a feedback servo signal 832to a servo control in the laser module 810 that processes this feedbackservo signal 832 to extract the information on the beam positioning andother properties of the beam on the screen 801. The servo controladjusts the direction and other properties of the scanning beam 820 toensure the proper operation of the display system.

The optical sensing unit 830 may be on the screen 801 or off the screen801 and includes at least one optical detector to detect one of the red,green and blue light emitted from the screen 801. In the illustratedexample, three optical detectors PD1, PD2 and PD3 are provided in thesensing unit 830 to detect the red, green and blue fluorescent light,respectively. Each optical detector is designed to receive light from apart of or the entire screen. A bandpass optical filter can be placed infront of each optical detector to select a designated color whilerejecting light of other colors.

FIG. 8B illustrates an example of a laser-based display system using ascreen having color phosphor stripes and an IR servo mechanism. Thesystem includes a laser module 810B to produce and project at least onescanning laser beam 820 onto a screen 801B. The screen 801B has parallelcolor phosphor stripes in the vertical direction and two adjacentphosphor stripes are made of different phosphor materials that emitlight in different colors. The laser beam 820 is at the wavelengthwithin the optical absorption bandwidth of the color phosphors and isusually at a wavelength shorter than the visible blue and the green andred colors for the color images. The laser module 810B can include oneor more lasers such as UV diode lasers to produce the beam 820, a beamscanning mechanism to scan the beam 820 horizontally and vertically torender one image frame at a time on the screen 801B, and a signalmodulation mechanism to modulate the beam 820 to carry the informationfor image channels for red, green and blue colors. Such display systemsin FIGS. 8A and 8B may be configured as rear projection systems wherethe viewer and the laser module 810B are on the opposite sides of thescreen 801B. Alternatively, such display systems may be configured asfront projection systems where the viewer and laser module 810B are onthe same side of the screen 801B.

A scanning display system can be calibrated during the manufactureprocess so that the laser beam on-off timing and position of the laserbeam relative to the fluorescent stripes in the screen 801B are knownand are controlled within a permissible tolerance margin in order forthe system to properly operate with specified image quality. However,the screen 801B and components in the laser module 801B of the systemcan change over time due to various factors, such as scanning devicejitter, changes in temperature or humidity, changes in orientation ofthe system relative to gravity, settling due to vibration, aging andothers. Such changes can affect the positioning of the laser sourcerelative to the screen 801B over time and thus the factory-set alignmentcan be altered due to such changes. Notably, such changes can producevisible and, often undesirable, effects on the displayed images. Forexample, a laser pulse in the scanning excitation beam 820 may hit asubpixel that is adjacent to an intended target subpixel for that laserpulse due to a misalignment of the scanning beam 820 relative to thescreen along the horizontal scanning direction. When this occurs, thecoloring of the displayed image is changed from the intended coloring ofthe image. Hence, a red pixel in the intended image may be displayed asa green pixel on the screen. For another example, a laser pulse in thescanning excitation beam 820 may hit both the intended target subpixeland an adjacent subpixel next to the intended target subpixel due to amisalignment of the scanning beam 820 relative to the screen along thehorizontal scanning direction. When this occurs, the coloring of thedisplayed image is changed from the intended coloring of the image andthe image resolution deteriorates. The visible effects of these changescan increase as the screen display resolution increases because asmaller pixel means a smaller tolerance for a change in position. Inaddition, as the size of the screen increases, the effect of a changethat can affect the alignment can be more pronounced because a largemoment arm in scanning each excitation beam 820 associated with a largescreen means that an angular error can lead to a large position error onthe screen. For example, if the laser beam position on the screen for aknown beam angle changes over time, the result is a color shift in theimage. This effect can be noticeable and thus undesirable to the viewer.

Implementations of various alignment mechanisms can be provided tomaintain proper alignment of the scanning beam 820 on the desiredsub-pixel to achieve desired image quality. These alignment mechanismsinclude reference marks on the screen, both in the fluorescent area andin one or more peripheral area outside the fluorescent area, to providefeedback light that is caused by the excitation beam 820 and representsthe position and other properties of the scanning beam on the screen.The feedback light can be measured by using one or more optical servosensors to produce a feedback servo signal. FIGS. 8A and 8B provide twoexamples for such feedback controls. A servo control in the laser module810B processes this feedback servo signal to extract the information onthe beam positioning and other properties of the beam on the screen and,in response, adjust the direction and other properties of the scanningbeam 820 to ensure the proper operation of the display system.

For example, a feedback servo control system can be provided to useperipheral servo reference marks positioned outside the display areaunobservable by the viewer to provide control over various beamproperties, such as the horizontal positioning along the horizontalscanning direction perpendicular to the fluorescent stripes, thevertical positioning along the longitudinal direction of the fluorescentstripes, the beam focusing on the screen for control the imagesharpness, and the beam power on the screen for control the imagebrightness. For another example, a screen calibration procedure can beperformed at the startup of the display system to measure the beamposition information as a calibration map so having the exact positionsof sub-pixels on the screen in the time domain. This calibration map isthen used by the laser module 810B to control the timing and positioningof the scanning beam 820 to achieve the desired color purity. For yetanother example, a dynamic servo control system can be provided toregularly update the calibration map during the normal operation of thedisplay system by using servo reference marks in the fluorescent area ofthe screen to provide the feedback light without affecting the viewingexperience of a viewer. The system in FIG. 8A uses the emitted coloredlight as the feedback for controlling beam alignment on the screen. FIG.8B shows another design that uses designated IR feedback light forcontrolling beam alignment on the screen.

In FIG. 8B, the laser module 810B also produces an invisible servo beam830 such as an IR beam and scans the servo beam 830 on to the screen801B along with the excitation beam 820. Different from the excitationbeam 820, the servo beam 830 is not modulated to carry image data. Theservo beam 830 can be a CW beam. The stripe dividers on the screen 801Bcan be made reflective to the light of the servo beam 830 and to producefeedback light 832 by reflection. The servo beam 830 has a known spatialrelation with the excitation beam 820. Therefore, the positioning of theservo beam 830 can be used to determine the positioning of theexcitation beam 820. This relationship between the servo beam andexcitation beams can be determined by using reference servo marks suchas a start of line mark in a non-viewing area of the screen 801B. Thelaser module 801B receives and detects the feedback light 832 to obtainpositioning information of the servo beam 830 on the screen 801B and usethis positioning information to control alignment of the excitation beam820 on the screen. The servo beam 830 is invisible and does not produceany noticeable visual artifact on the screen 801B during the normaloperation of the system when images are produced on the screen 801B. Forexample, the servo beam 830 can have a wavelength in a range from 780 nmto 820 nm. For safety concerns, the screen 801B can be made to have afilter that blocks the invisible servo beam 830 from exiting the screen801B on the viewer side. In this regard, a cutoff absorbing filter witha bandpass transmission range only in the visible spectral range (e.g.,from 420 nm to 680 nm) may be used to block the servo beam 830 andexcitation beam 820. The servo control of the excitation beam 820 basedon the servo beam 830 can be performed dynamically during the normaloperation of the system. This servo design avoids manipulation of theimage-producing excitation beam 820 during the normal display mode forservo operations and thus avoids any visual artifacts that may be causedby the servo-related manipulation of the image-producing excitation beam820.

In addition, in some implementations, the scattered or reflectedexcitation light by the screen 801B may also be used for servo controloperations during a period when the system does not show images, e.g.,during the startup period of the system or when the excitation beam 820is outside the active display area of the screen 801B. In such a case,the scattered or reflected excitation light, labeled as light 822, canbe used as servo feedback light for servo control of the horizontalalignment of each laser. This is different from the design as in FIG. 8Awhere emitted colored light from the phosphors on the screen (ratherthan the excitation light) is used as the feedback light for thealignment feedback control.

In some implementations based on the invisible servo beam 830, the servobeam 830 can be directed along with the one or more excitation beams 820through the same optical path. The servo beam 830 is invisible and canbe overlapped with a scanning path of one excitation beam 820 or alongits own scanning path that is different from a path of any of theexcitation beams 820. The spatial relation between the servo beam 830and each excitation beam 820 is known and fixed so that the positioningof the servo beam 830 on the screen 801B can be used to inferpositioning of each excitation beam 820.

A light source for generating the servo beam 830 and a light source forgenerating an excitation beam 820 can be semiconductor lasers in a lightsource module which can be an array of lasers and at least one of thelasers in the laser array can be a servo laser that produces the servobeam 830. The location of the servo laser is known relative to eachexcitation laser. The servo beam 830 and each excitation beam 820 aredirected through the same relay optics, the same beam scanners and thesame projection lens and are projected on the screen 801B. Therefore,the positioning of the servo beam 830 on the screen 801B has a knownrelation with the positioning of each excitation beam 820 on the screen.This relation between the servo beam 830 and each excitation beam 820can be used to control the excitation beam 820 based on measuredpositioning of the servo beam 830.

FIG. 8C illustrates a scanning beam display system based on a servocontrol using the invisible servo beam 830 as one exemplaryimplementation of the design in FIG. 8B. A display processor andcontroller 840 can be used to provide control functions and controlintelligence based on servo detector signals from radiation servodetectors 850 that detect servo feedback light 832 from the screen 801B.A single detector 850 may be sufficient and two or more servo detectors850 can be used to improve the servo detection sensitivity. Similarly,one or more radiation servo detectors 860 may also be used to collectexcitation servo light 822 produced by scattering or reflecting theexcitation beam 820 at the screen to provide additional feedback signalsto the processor and controller 840 for the servo control. A scanningprojection module 870 is provided to scan and project the excitation andservo beams 820 and 830 onto the screen 801B. The controller 840includes a circuit that produces scanning control signals to thescanning module 870 for controlling the beam scanning, such as thecurrent to the conductor coil in the flexure actuator. As illustrated,the image data is fed to the display processor and controller 840 whichproduces an image data signal carrying the image data to a signalmodulator controller 880 for excitation lasers 881. The servo laser,which may be positioned among the excitation lasers 881, is notmodulated to carry image data. The signal modulation controller 880 caninclude laser driver circuits that produce laser modulation signalscarrying image signals with image data assigned to different lasers 881,respectively. The laser control signals are then applied to modulate thelasers 881, e.g., the currents for laser diodes to produce the laserbeams 882. The display processor and controller 840 also produces lasercontrol signals to the lasers in the lasers 881 to adjust the laserorientation to change the vertical beam position on the screen 801B orthe DC power level of each laser. The display processor and controller840 further produces scanning control signals to the scanning projectionmodule 870 to control and synchronize the horizontal polygon scanner andthe vertical scanner (which can include the flexure actuator).

In each horizontal scan, the beam 820 or 830 scans across thelight-emitting stripes and the reflections produced by the stripedividers can be used to indicate horizontal positions of the stripedividers, spacing between two adjacent stripe dividers and horizontalpositions of the horizontally scanned beam 820 or 830. Therefore,reflections from the stripe dividers can be used for servo control ofthe horizontal alignment between the beam 820 and the light-emittingstrips.

Based on the stripe divider and possibly other reference marks, such asperipheral reference marks outside the active display area of thescreen, the positioning of the servo beam 830 on the screen 801B can bemeasured. Because the servo beam 830 has a fixed relation with eachexcitation beam 820, any error in the positioning of the servo beam 830suggests a corresponding error in each excitation beam 820. Therefore,the positioning information of the servo beam 830 can be used in theservo control to control the servo beam 830 and each excitation beam 820to reduce an alignment error of the excitation beam.

The present servo control operates to place each optical pulse in theexcitation beam 820 near or at the center of a target light-emittingstripe to excite the light-emitting material in that stripe withoutspilling over to an adjacent light-emitting stripe. The servo controlcan be designed to achieve such alignment control by controlling thetiming of each optical pulse in order to place the pulse at a desiredposition on the screen 801B during a horizontal scan. Accordingly, theservo control, i.e., the processor and controller 640, needs to “know”horizontal positions of the light-emitting stripes in each horizontalline before each horizontal scan in order to control the timing ofoptical pulses during the scan. This information on horizontal positionsof the light-emitting stripes in each horizontal line constitutes atwo-dimensional position “map” of the active display area orlight-emitting area of the screen 801B of (x, y) coordinates where x isthe horizontal position of each stripe divider (or equivalently, thehorizontal position of the center of each stripe) and y is the verticalposition or ID number of a horizontal scan. This position map of thescreen 801B can be measured at the factory and may change in time due tochanges in the system components due to temperature, aging and otherfactors. For example, thermal expansion effects, and distortions in theoptical imaging system will need corresponding adjustments in theprecise timing to activate each color in a pixel. If the laser actuationdoes not properly correspond to the timing where the beam is directed atthe central portion of a sub-pixel or stripe for the intended phosphor,the beam 820 will either partially or completely activate the wrongcolor phosphor. In addition, this position map of the screen 801B canvary from one system to another due to the component and devicetolerances during the manufacturing.

Therefore, it is desirable to update the position map of the screen 801Band to use the updated position map for controlling the timing of pulsesof the excitation beam 820 in each horizontal scan during the normaldisplay. The position map of the screen 801B can be obtained using thefeedback light 822 and 832 in a calibration scanning when the system isnot in the normal display mode, e.g., during the start-up phase of thesystem. In addition, the servo feedback light 832 can be used in realtime video display to monitor and measure changes in an existingposition map of the screen 801B when the system is operating in thenormal display mode to produce images on the screen 801B. This mode ofthe servo control is referred to as dynamic servo. The dynamicmonitoring of the screen 801B can be useful when the system operates foran extended period time without a downtime because the screen 801B mayundergo changes that can lead to significant changes to the position mapof the screen 801B that is updated during the start-up phase of thesystem.

Hence, based on FIGS. 8B and 8C, the servo control can be provided usingthe servo beam 830 during the normal display mode when each excitationbeam 820 is used for carrying optical pulses for producing images on thescreen 801B and is not used for servo control. The servo beam 830 is aCW beam and is scanned over one horizontal line per screen segment withthe scanning modulated excitation Laser beams 820. The servo feedbacklight 832 is detected by the one or more servo detectors 850 to measurean alignment error of the servo beam 830 on the screen 801B during thenormal display. The alignment of each excitation laser beam 820 isadjusted based on the measured alignment error of the servo beam 830 toreduce the alignment error of the excitation laser beam 820.

Examples of feedback controls for various scanning display systems aredisclosed in PCT publication No. WO 2007/095329 entitled “SERVO-ASSISTEDSCANNING BEAM DISPLAY SYSTEMS USING FLUORESCENT SCREENS” and publishedon Aug. 23, 2007, U.S. Patent Publication No. 20070188417 entitled“SERVO-ASSISTED SCANNING BEAM DISPLAY SYSTEMS USING FLUORESCENT SCREENS”and published on Aug. 16, 2007, U.S. Patent Publication No. 20100097678entitled “SERVO FEEDBACK CONTROL BASED ON DESIGNATED SCANNING SERVO BEAMIN SCANNING BEAM DISPLAY SYSTEMS WITH LIGHT-EMITTING SCREEN” andpublished on Apr. 22, 2010, and U.S. Pat. No. 7,878,657 entitled “SERVOFEEDBACK CONTROL BASED ON INVISIBLE SCANNING SERVO BEAM IN SCANNING BEAMDISPLAY SYSTEMS WITH LIGHT-EMITTING SCREENS” and issued Feb. 1, 2011,all of which are incorporated by reference as part of the disclosure ofthis document.

FIGS. 9A and 9B show an exemplary design of the screen 801 of FIGS. 8AAND 8B that uses a light-emitting fluorescent layer with differentlight-emitting regions that emit visible light by absorbing excitationlight such as UV light. In this particular example, the light-emittingregions are parallel stripes (e.g., phosphor stripes) and the opticalmodule 810 is provided to scan laser excitation light 820 modulated withoptical pulses through the stripes to produce pixilated images.

FIG. 9A shows the operation of the screen 101 in a view along thedirection B-B perpendicular to the surface of the screen in FIG. 9B. Aset of adjacent light-emitting stripes of different colors, e.g., redlight (R), green light (G) and blue light (B), are grouped to togetherto form a color pixel and each stripe within the set forms a subcolorpixel. In operation, each of the one or more laser beams 820 is scannedspatially across the light-emitting screen 801 to hit different colorpixels at different times. Accordingly, the modulated beam 820 carriesthe image signals for the red, green and blue for each pixel atdifferent times and for different pixels at different times. Hence, themodulation of the beam 820 is coded with image information for differentpixels at different times to map the timely coded image signals in thebeam 820 to the spatial pixels on the screen 801 via the beam scanning.The beam scanning converts the timely coded image signals in form ofoptical pulses into spatial patterns as displayed images on the screen101.

Since each phosphor stripe for emitting light of a particular color islongitudinal in shape, the cross section of the beam 820 may be shapedto be elongated along the direction of the stripe to maximize the fillfactor of the beam within each color stripe for a pixel. This may beachieved by using a beam shaping optical element in the laser module810. A laser source that is used to produce a scanning laser beam thatexcites a phosphor material on the screen may be a single mode laser ora multimode laser. The laser may also be a single mode along thedirection perpendicular to the elongated direction phosphor stripes tohave a small beam spread that is confined by the width of each phosphorstripe. Along the elongated direction of the phosphor stripes, thislaser beam may have multiple modes to spread over a larger area than thebeam spread in the direction across the phosphor stripe. This use of alaser beam with a single mode in one direction to have a small beamfootprint on the screen and multiple modes in the perpendiculardirection to have a larger footprint on the screen allows the beam to beshaped to fit the elongated color subpixel on the screen and to providesufficient laser power in the beam via the multimodes to ensuresufficient brightness of the screen.

Referring to FIG. 9B, the screen 801 includes a rear substrate 801 whichis transparent to the scanning laser beam 820 and faces the laser module810 to receive the scanning laser beam 820. A second front substrate 202is fixed relative to the rear substrate 201 and faces the viewer in arear projection configuration. A color phosphor stripe layer 203 isplaced between the substrates 201 and 202 and includes phosphor stripes.The color phosphor stripes for emitting red, green and blue colors arerepresented by “R”, “G” and “B,” respectively. The front substrate 202is transparent to the red, green and blue colors emitted by the phosphorstripes. The substrates 201 and 202 may be made of various materials,including glass or plastic panels. Each color pixel includes portions ofthree adjacent color phosphor stripes in the horizontal direction andits vertical dimension is defined by the beam spread of the laser beam820 in the vertical direction. As such, each color pixel includes threesubpixels of three different colors (e.g., the red, green and blue). Thelaser module 810 scans the laser beam 820 one horizontal line at a time,e.g., from left to right and from top to bottom to fill the screen 801.The laser module 810 is fixed in position relative to the screen 801 sothat the scanning of the beam 820 can be controlled in a predeterminedmanner to ensure proper alignment between optical pulses in the laserbeam 820 and each pixel position on the screen 801. As illustrated, thescanning laser beam 820 is directed at the green phosphor stripe withina pixel to produce green light for that pixel.

The systems in FIGS. 8A and 8B with the screen design in FIGS. 9A and 9Bcan be operated by controlling the pixels to display a pattern or imageone frame at a time and to display consecutive frames over time at asuitable frame rate, e.g., 24 frames per second, 30 frames per second,60 frames per second, 120 frames per second or 240 frames per second.Each frame is formed by controlled illumination of the pixels by variousscanned illumination methods. For example, a frame can be constructed bya progressive scanning to illuminate pixels in one row at a time andsequentially scan through all rows. For another example, a frame can beconstructed by an interlaced scanning to illuminate pixels in one row ata time and progressively scan through only odd-numbered rows at firstand then progressively scan through only even-numbered rows.

Beam scanning can be performed in various ways by the scanning module810 in FIGS. 8A and 8B. FIG. 10 illustrates an example of simultaneousscanning of one screen segment with multiple scanning laser beams at atime and sequentially scanning consecutive screen segments. Visually,the beams 820 behaves like a paint brush to “paint” one thick horizontalstroke across the screen 801 at a time to cover one screen segment andthen subsequently to “paint” another thick horizontal stroke to cover anadjacent vertically shifted screen segment. Assuming the laser array inthe module 810 has 36 lasers, a 1080-line progressive scan of the screen801 would require scanning 30 vertical screen segments for a full scan.Hence, this configuration in an effect divides the screen 801 along thevertical direction into multiple screen segments so that the N scanningbeams scan one screen segment at a time with each scanning beam scanningonly one line in the screen segment and different beams scanningdifferent sequential lines in that screen segment. After one screensegment is scanned, the N scanning beams are moved at the same time toscan the next adjacent screen segment. In some implementations, onefacet of the polygon can be used to scan one screen segment withmultiple scanning laser beams at a time and the next polygon facet isused to scan the next screen segment. In this mode, the vertical scanneradjusts the vertical positions of all beams at the end of scanning eachscreen segment by one polygon facet to scan the next screen segment bythe next polygon facet.

Therefore, the N diode lasers produce modulated laser excitation beamsof the excitation light at the single excitation wavelength, onemodulated laser excitation beam from each diode laser per one lasercurrent control signal carrying images of different colors in therespective laser current control signal. The beam scanning scans,simultaneously and along the direction perpendicular to the phosphorstripes, the modulated laser excitation beams on to the display screenat different and adjacent screen positions along the longitudinaldirection of the phosphor stripes in one screen segment of the displayscreen, to produce different scan lines, respectively, in the screensegment, to cause fluorescent layer of the display screen to emit lightof red, green and blue colors at different times at different positionsin each scan line and, to shift, simultaneously, the modulated laserexcitation beams to other screen segments at different positions in thedisplay screen along the vertical direction, one screen segment at atime, to render the images.

Hence, FIGS. 8A and 8B show exemplary display systems with a displayscreen that includes a fluorescent layer that absorbs an excitationlight at a single wavelength and emits visible light. The fluorescentlayer includes a plurality of parallel fluorescent stripes elongatedalong a first direction (e.g., the vertical direction) and spaced fromone another along a second direction perpendicular to the firstdirection (e.g., the horizontal direction). At least three adjacentfluorescent stripes are made of three different fluorescent materials: afirst fluorescent material that absorbs the excitation light and emitslight of a first color, a second fluorescent material that absorbs theexcitation light and emits light of a second color, and a thirdfluorescent material that absorbs the excitation light and emits lightof a third color. Such a system can include a plurality of diode lasersthat respond to respective laser current control signals to producemodulated laser excitation beams of the excitation light, one modulatedlaser excitation beam from each diode laser per one laser currentcontrol signal carrying images in the respective laser current controlsignal, a controller that generates the laser current control signalsthat respectively carry images and are applied to the one or more diodelasers; and a beam scanning mechanism. This beam scanning mechanismreceives the modulated laser beams and scans, along the seconddirection, the modulated laser excitation beams on to the display screenat different and adjacent screen positions along the first direction inone screen segment of the display screen, to produce different scanlines along the second direction, respectively, in the screen segment,to cause the display screen to emit light of the first, second and thirdcolors at different times at different positions in each scan line alongthe second direction and, to shift, simultaneously, the modulated laserexcitation beams to other screen segments at different positions in thedisplay screen along the first direction, one screen segment at a time,to render the images.

In the above designs with multiple laser beams, each scanning laser beamscans only a number of lines across the entire screen along the verticaldirection that is equal to the number of screen segments, and, withineach screen segment, several beams simultaneously scan multiple lines.Hence, the polygon scanner for the horizontal scanning can operate at aslower speed than a scanning speed needed for a single beam scan designthat uses the single beam to scan every line of the entire screen. For agiven number of total horizontal lines on the screen (e.g., 1080 linesin HDTV), the number of screen segments decreases as the number of thelasers increases. Hence, in a system that uses 36 lasers to produce 36excitation laser beams, the galvo mirror and the polygon scanner scan 30lines per frame while a total of 108 lines per frame are scanned whenthere are only 10 lasers. Hence, the use of the multiple lasers canincrease the image brightness which is approximately proportional to thenumber of lasers used and, at the same time, can also advantageouslyreduce the response speeds of the scanning module.

Polygons can be designed to have polygon facets with the identical facetorientation. When such a polygon is used for the horizontal scanning,the vertical scanning is entirely achieved by the vertical adjustment ofthe vertical scanner. Hence, in the scanning example in FIG. 10, thevertical scanner needs to change its orientation at the end of thescanning by each polygon facet since two adjacent polygon facets areused to scan to adjacent vertical screen segments. Alternatively, apolygon can be designed to have different reflective polygon facetstilted at different tilt facet angles which increase or decrease by afixed amount sequentially from one facet to another. Such a polygon is a2-dimensional polygon because an input beam with a fixed direction ororientation when scanned by this polygon produces a series of differenthorizontal scan lines on the screen that are spaced along the verticaldirection as if the beam is scanned along both the horizontal andvertical directions.

One implementation for using the combination of the vertical scanner andpolygon scanner in the system in FIG. 8A or FIG. 8B is based on atwo-dimensional polygon scanner with different reflective polygon facetstilted at different tilt facet angles. In this implementation, rotationsof the polygon scanner are used to scan optical beams horizontallywithout simultaneous vertical scanning to produce horizontal scan lineson the screen and adjust vertical positions of the optical beams duringa blanking time when there is no light projected onto the screen byusing different facets. In some implementations, the vertical scanner isfixed in position during a full rotation of the polygon and this is notoperated as a “scanner” but rather as a vertical position adjuster. Thisvertical scanner or adjuster, e.g., the device 750 in FIGS. 7A, 7B and7C, can be used in combination with the two-dimensional polygon scannerto provide an additional vertical adjustment to the vertical positionsof the beams during a blanking time when there is no light projectedonto the screen to increase the number of horizontal lines on thescreen.

This vertical adjuster can include a reflector to reflect each beam andan actuator such as the flexure actuator in FIGS. 1-4B to control theorientation of the reflector to adjust the vertical position of a beamon the screen. The vertical adjuster is operated to hold the verticalposition of a beam at a fixed vertical position on the screen when thebeam is being horizontally scanned on the screen. During the horizontalscanning by each facet of the polygon, the vertical adjuster in suchimplementations does not perform vertical scanning due to the operationof the two-dimensional polygon scanner. Therefore, this design can beused to lessen the technical performance parameters for the verticaladjuster in comparison with a vertical scanner and to allow a variety ofbeam deflection devices with adjust actuators to be used as the verticaladjuster, such as various 1-dimensional beam scanners, reflectorscoupled with step actuators and others, to be used in scanning displaysystems based on the two-dimensional polygon scanner described in thisdocument. As a specific example, a beam deflector having a reflectivemirror and a sweeping or step galvanometer actuator engaged to themirror may be used to implement the vertical adjuster.

In operation, the polygon scanner rotates to scan the scanning beams.Each polygon facet receives, reflects and scans the beams 820simultaneously and horizontally on the screen 801 within one screensegment. The immediate next polygon facet is tilted at a different tiltangle and thus receives, reflects and scans the same beams 820simultaneously and horizontally at different vertical positions on thescreen 801 in another screen segment next to the previous screen segmentalong the vertical direction. The different optical beams 820 from onepolygon facet are directed to different vertical positions on the screen801. As different polygon facets sequentially take turns to perform thehorizontal scanning of the beams 820 as the polygon scanner rotates, thevertical positions of beams 820 on the screen 801 are stepped verticallyat different positions along the vertical stepping direction without anyscanning along the vertical direction to change the position of eachbeam during each horizontal scan because the vertical adjuster isoperated at a fixed orientation.

FIG. 11A illustrates one example for interlaced raster scanning for the2D polygon scanner and the vertical adjuster. Assume there are M facetsin the polygon and N optical beams 810. The tilt facet angles of thepolygon facets can be designed to vertically divide the screen into Mvertical segments to project N parallel horizontal scan lines in eachvertical segment. In some implementations, the line spacing between twoadjacent lines of the N lines can be set to allow for at least onehorizontal scan line and this configuration can be used to supportinterlaced scanning operations. As the polygon rotates, different facetsdirect and scan different vertical segments at different times, one at atime. Hence, scanning by different polygon facets in one full rotationof the polygon scanner produces a frame or field of M×N horizontalscanning lines that are made of M sequential sets of N simultaneoushorizontal lines. This operation provides both horizontal scanning byeach facet and vertical stepping by sequentially changing the polygonfacets. Therefore, in one full rotation, the polygon scanner producesone frame of a sequential sets of simultaneous horizontal scanning lineson the screen produced by the polygon facets, respectively and eachpolygon facet produces one set of simultaneous and horizontal scanninglines.

Notably, during each full rotation, the vertical adjuster is controlledat a fixed orientation. After completion of one full rotation of thepolygon and before the next full rotation of the polygon, the verticaladjuster is operated to adjust its orientation to change verticalpositions of the optical beams 12 on the screen 801 to spatiallyinterlace horizontal scanning lines in one frame produced in one fullrotation of the polygon scanner with horizontal scanning lines of asubsequent frame produced in an immediate subsequent full rotation ofthe polygon scanner. The vertical adjuster and the polygon scanner aresynchronized to each other to perform the above interlaced rasterscanning. In the example in FIG. 11A, each full frame image is formed bytwo frames or fields, Field 1 and Field 2, that are spatially interlacedand the line spacing between two adjacent lines produced by each facetis one horizontal scan line to facilitate the interface operation.Hence, the vertical adjuster in this example is operated to operate attwo orientations, one orientation for the Field 1 and another for theField 2, respectively. In this specific example, the rate for thevertical adjustment of the beam position is only two orientationadjustments per full frame that is produced by two full rotations of thepolygon.

Interlacing two image fields is illustrated in the example in FIG. 11A.The spacing between two adjacent lines on the screen produced byreflection of beams from a single polygon facet can be set to (P−1)where P is the number of fields to be interlaced and is an integer notless than 2. Hence, the spacing between the scanning lines on the screenformed by two adjacent laser beams reflected from a one polygon facetcan be one horizontal line for interlacing two fields and two horizontallines for interlacing three fields.

In addition, the vertical adjuster can be used to stack two or moredifferent image fields along the vertical stepping direction to form afull image. The control unit is configured to control the verticaladjuster to scan the optical beams over a first surface segment at afirst fixed position of the vertical adjuster in a full rotation of thepolygon scanner and to scan the optical beams over a second surfacesegment that is vertically displaced from and does not overlap with thefirst surface segment when the vertical adjuster is at a second fixedposition in a subsequent full rotation of the polygon scanner.

FIG. 11B shows an example of this operation mode of the verticaladjuster. In this example, one full rotation of the polygon producesField 1 with N×M parallel horizontal lines as shown. Next, the verticaladjuster is operated during a blanking time before the next scanning forthe field 2 to move the vertical positions of the beams to produce thefiled 2 below the field 1. At the end of this blanking time, the lightof the beams is turned on to allow the polygon scanner to project N×Mparallel horizontal lines for the filed 2. This operation allows animage of 2×N×M horizontal lines to be formed on the screen.

In the above and other scanning operations, the vertical beam pointingaccuracy is controlled within a threshold in order to produce a highquality image. When multiple scanning beams are used to scan multiplescreen segments, this accuracy in the vertical beam pointing should becontrolled to avoid or minimize an overlap between two adjacent screensegments because such an overlap in the vertical direction can severelydegrade the image quality. The vertical beam pointing accuracy should beless than the width of one horizontal line in implementations.

FIG. 12 illustrates two different types of beam positioning errors onthe screen 801 along the horizontal and vertical directions caused bythe galvo position error where the galvo mirror is based on the flexureactuator in FIGS. 1-4B and the scanning in FIG. 11A. The flexureactuator executes high-speed, small-angle movements between two fixedmirror positions for the interlaced scanning shown in FIG. 11A. Thismovement should be performed with very little off-axis motion in theflexure actuator to ensure high quality image quality on the screen. Afeedback control can be provided to accurately control the movement ofthe flexure actuator.

In various applications where precise control of orientation andposition of an optical beam are desired, a positioning sensor can beprovided to measure and monitor the positioning of either the flexureactuator or the mirror that is engaged to and controlled by the flexureactuator. The positioning measurement is conducted in real time duringoperation of the flexure actuator and is fed into a servo control thatuses the positioning measurement to correct any positioning error in theflexure actuator and to ensure the proper positioning of the flexureactuator within the specified positioning precision range. FIGS. 5A and5B described above provide an example of an optical positioning sensingdesign for the servo control. Other positioning sensing mechanisms mayalso be implemented. The following sections provide an example based oncapacitor positioning sensing for the flexure actuator described inFIGS. 1-4B.

FIGS. 13A, 13B and 13C illustrate the general structure and location ofan exemplary capacitor positioning sensing design for the flexureactuator in FIGS. 1-4B. A capacitor position sensor is integrated to theflexure assembly to measure the position of the mirror platform 130 andthe measured position is used by the servo control to control theflexure motor by controlling the current in the coil in interaction withthe magnets. A movable charge plate, also shown as cap sensor movingplate in other figures, is fixed to the mirror platform 130 and isinserted between the gap between the two capacitor conductive plates asthe position sensor. Referring to FIGS. 13A and 13B, upper and lowercapacitance sensor charge plates are shown on one side of the mirrorplatform 130. Upper and lower insulator plates are provided to supportupper and lower capacitor conductive plates for the sensing capacitorand the upper and lower capacitance sensor charge plates. FIG. 13C showsthe structure from another view to show the exposed movable charge platethat has a bended structure for mounting to the mirror platform 130 andfor extending beneath of the mirror platform 130.

FIGS. 14A and 14B further show various structures associated with theflexure for the flexure actuator and various structures associated thecapacitor sensor plate. The mirror platform 130 is mounted on top of theflexure actuator and its position and motion are controlled by theflexure actuator. The flexure has a structure that is different from theflexure shown in FIG. 4B. One of the four flexure extensions in FIG. 4Bhas been modified as an electrically conductive charge plate mountingarm 1 that connects to the movable charge plate and is parallel to otherthree remaining flexure extensions of the flexure actuator. A bottomcharge plate mount base that extends substantially perpendicular to thecharge plate mounting arm 1 is provided and is an extended part of thecharge plate mounting arm 1. The bottom charge plate mount base providesthe mechanical support and rigidity, and a mounting or anchoring forattaching to the base molding. The bottom charge plate mount base alsoforms part of the electrical path formed by the charge plate mountingarm 1. In combination with the bottom charge plate mount base, thecharge plate mounting arm 1 provides (1) mechanical support andrigidity, (2) a mounting or anchoring for attaching the movable chargeplate to the mirror platform 130, and (3) an electrical conductive pathto apply a sensor signal to the movable charge plate for the positionsensing operation. On the other side of the movable charge plate, asecond short charge plate mounting arm 2 is formed as an integrated partof the movable charge plate to provide another mounting and anchoringpart to the bottom of the mirror platform 130. Notably, since the otherflexure extension that is in parallel to the charge plate mounting arm 1and is close to the movable charge plate provides the electrical supplypath for the current in the coil, electrical isolation is providedbetween this electrical path and the electrical path for the capacitorsensing operation. As illustrated in FIG. 14B, an insulation orseparation gap is formed between the bottom charge plate mount base andthe bottom flexure base so that the structure formed by the bottomcharge plate mount base, the charge late mounting arm 1, the movablecharge plate and the charge plate mount 2 is electrically insulated fromthe flexure structure. As such, the magnetic coil current that goingthrough the flexure part is insulated from any electrical conductivepart for the capacitor sensing structure.

FIG. 15 shows additional structural details of the above design. Alsoshown in FIG. 15 is a bending part between the charge plate mounting arm1 and the movable charge plate for engagement contact to end side facetof the mirror platform 130. An adhesive or other engagement means can beused to fix this bending part to the side facet of the mirror platform130. FIG. 15 also provides various views of different parts of thedesign.

FIG. 16 shows mounting of upper and lower insulator plates by usingorientation adjustment set screws (e.g., A, B and C) to ensure thecapacitor plates are parallel to the movable charge plate engaged to themirror platform 130. The adjustment set screws can be engaged tothreaded holes in the underneath motor frame which may a die castmodule.

FIGS. 17, 18 and 19 illustrate an example of the circuit design andoperation of the position sensing and servo control.

The movable charge plate between the upper and lower capacitor platescan change electrical charges on the upper and lower capacitor platesdepending on its respective distances to the upper and lower capacitorplates. This structure forms two varying capacitors Ca and Cb as shownin the circuit in FIG. 18. The capacitance values of the capacitors Caand Cb change with the position of the movable charge plate whichdepends on the position of the mirror platform 130 driven by the flexureactuator. An oscillation signal source, e.g., a 200 KHz signal source asshown in FIG. 18, is used to generate and apply a sensor signal to thecenter charge plate. In presence of this sensor signal, two voltageoutput signals VA and VB are generated and the differential signalbetween VA and VB is produced as the output of the capacitor sensor. Twocharge amplifiers connected to the respective pick up plates convert theinput capacitance modulations to the voltage modulated signals VA andVB. Consider the example where the center charge plate in FIG. 18 isdriven with a 200 Khz sine wave. Assuming the plate moves about 5 um for0.06 degree of galvo rotation, the two voltages on the two plates areVA(x)=Vin*Ca(x)/Cf and VB(x)=Vin*Cb(x)/Cf where x is the positionparameter. The differential signal between VA and VB is the positionsignal and the sum signal of VA and VB is used to linearize andnormalize the position signal (VA−VB). FIG. 19 shows examples of relatedsignals based on VA and VB in a sample flexure actuator.

Based on the amplitude modulated (VA−VB) signal, the signal can bedemodulated either using an analog technique or digital technique.

In the analog demodulation, the modulated position signal VA−VB can befiltered by a bandpass filter to eliminate the low frequency noise andcoupling components from the coil drive into the pick up plates. Thefiltered signal is then demodulated (recover the low frequency envelopesignal) by sampling both the positive and negative peaks of VA−VB withseparate track hold circuits that hold each value for ¾ of a cycle. Theposition signal can then be recovered by inverting one of the heldsignals and then switching between each every half cycle.

FIG. 20 shows an example circuit for the above operation. The sum signalis used to regulate the 200 Khz Sine Wave magnitude and linearize thePosition signal. The AGC forces the Sum signal to equal Sum_Ref bycontrolling the 200 Khz Sine amplitude and can be disabled allowing theSum_Ref signal to manually set the Sine amplitude.

FIG. 21 shows an example of a digital circuit for digital demodulation.In this circuit, the differential signal (VA−VB) is synchronouslydemodulated by sampling both positive and negative peaks using an ADCconverter and then demodulate in the FPGA. In demodulation, the negativepeak value is inverted and the inverted value is added to the positivepeak value. Using both positive and negative peaks cancels ADC samplingerrors and improves signal to noise. Both peaks are averaged to producea single sample. In the digital circuit in FIG. 21, sampling and sinegeneration clocks are synchronized. A one-time calibration can beperformed to adjust the sampling times vs. the 200 Khz reference clockused to generate the charge plate sine wave. The 200 Khz reference clockis converted to a sine wave using a Band Pass Filter and analog switches

FIG. 22 shows an example of a servo circuit based on the output from thecapacitor sensor. The galvo assembly is part of a servo control loop.The servo loop uses a capacitive position detector (CPD) to control theangle of the galvo mirror. A Position command (POS CMD) and a FeedForward waveform are synchronized to perform the closed loop scanningmoves. Also shown in the figure are the screen illumination lasers thatare positioned on the display screen based on galvo angle. The servoloop can be designed for 0 dB cross-over at 2 KHz or for other operatingfrequency ranges. The galvo mirror can be operated by the flexureactuator to switch between two galvo positions for the interlacedscanning of multiple laser beams as described above. At each of the twogalvo positions, the capacitor sensor and the servo control loop operateto accurately maintain the galvo position based on the positionmeasurements from the capacitor sensor.

Consider, for example, an implementation of the system in FIG. 8A or 8Bwhere the galvo is required to move 0.06 degrees in 240 μs and settleand remain within +/−0.0006 degrees over the next 4 ms of the frametime. The flexure actuator needs to provide a high-speed motion tochange the mirror position from the first position A to the secondposition B in the required time and needs to minimize the residualmotion. A trajectory with a sinusoidal motion profile can be used toachieve this operation since the sinusoidal motion profile can be usedto provide a low jerk to the mechanical suspension of the presentflexure actuator design due to lack of step-like abrupt changes in themotion profile. In various implementations, this feature of thesinusoidal motion profile or other motion profile can be advantageousbecause the step in the driving current of the coil of the flexureactuator may undesirably cause a step change in the galvo torque andthis step change may excite undesired mechanical suspension modes. Asinusoidal trajectory minimizes this step and therefore minimizes theexcitation of mechanical resonant modes in the galvo. The sinusoidalmotion trajectory can also be desirable since it is well suited for feedforward servo design. In this approach, a pre-determined coil currentfor performing the move is first generated as part of the feed forwardand the servo is used to provide a correction term based on the servoerror feedback. The feed forward waveform is generated using the motiontrajectory equations of position, velocity, and acceleration vs time,and also the electro-mechanical model of the galvo.

The above described capacitor sensing and the flexure actuator structurecan be implemented in various configurations. For example, the describedfeatures can be used to construct a small rotation angle position,single axis, external electro magnetic field independent, differentialcapacitor sensor where the external electro magnetic field is sourced inproximity to the differential capacitor sensor, and where both theelectro magnetic field and the differential capacitor sensor areoperating with a substantially equal peak to peak voltage. The capacitordrive signal can be an oscillation signal at a frequency of about 200KHz.

For another example, the structures described above can be used toconstruct a less than 2% inertia contribution charge plate extension ofa differential capacitor sensor feedback system, where the charge plateextension extends beyond the impulse driven platform controlled by thefeedback system, where the charge plate extension contributes less than2% to modes in each axis of motion, where the differential capacitorsensor feedback system includes at least two pickup plates, and wherethe charge plate extension is bonded by an adhesive or other means tothe impulse driven platform until the extension is in proximity to thedual pickup plates. In implementations, the dual pickup plates can beaffixed to a common ground and a baseplate. The impulse driven platformis affixed with a mirror for directing light based on the motion of theplatform. The at least two pickup plates can be, for example, onopposite sides of the charge plate extension. The charge plate extensioncan be designed to move in proximity to the differential capacitorsensor feedback system. The impulse driven platform can move in asubstantially rotational direction.

For yet another example, the above described features can be used toform an impulse drive platform, where the platform supports a mirror andone or more components of a servo detection system, where the servodetection system is independent of reflections off the mirror. Theimpulse drive platform is part of a single dimensional movement axisflexure and one or more components of the servo detection system is acharge plate extension. The charge plate extension is the singledimensional movement axis flexure. The impulse drive platform comprisestwo pairs of flexures where one pair of flexures comprises two distinctand isolated from each other that conduct to different electricalsignals.

As an alternative to the above described capacitor sensing in FIGS. 13Athrough 17, FIGS. 23A, 23B and 23C illustrate an example of a chargedgrating capacitor sensing design for measuring and controlling thepositioning of the mirror platform supported by the flexure actuator110. In this design, a mirror platform 2310 is provided to include agrating facet 2312 on one side of the platform 2310. Referring to theexpanded view in FIGS. 23B and 23C, the grating facet 2312 includesmirror platform grating teeth 2316 which can be arranged to be spacedfrom one another periodically along the grating facet 2312.Corresponding to the grating facet 2312, a side grating module 2320 isengaged to a support base at the grating facet side of the mirrorplatform 2310. The side grating module 2310 includes a side gratingsupport structure or plate 2324 that is fixed to the support base at afixed position, and a side grating top plate 2321 that extends towardsthe mirror platform 2310 and has a matching grating facet 2322 thatfaces the grating face 2312 and is separated by a small gap as shown inFIGS. 23A, 23B and 23C. Referring to FIGS. 23B and 23C, the gratingfacets 2312 and 2322 are structured to be electrically conductive (e.g.,formed of a metal electrode) and have periodic grating teeth 2316 and2326, respectively. The periodic grating teeth 2316 and 2326 may bestructured so that the grating teeth 2316 on the mirror platform 2310match the geometry of the grating teeth 2326 on the side grating topplate 2322, e.g., both have the same period and shape. The periodicgrating teeth 2316 on the mirror platform 2310 form one electricallyconductive piece or are electrically connected to one another, andsimilarly, the grating teeth 2326 on the side grating top plate 2322form another electrically conductive piece or are electrically connectedto one another. The small gap between the grating facets 2312 and 2322is sufficiently small to allow the grating facets 2312 and 2322 toelectrically coupled to form a capacitor therebetween. The capacitancebetween the opposing periodic grating teeth 2316 and 2326 is measured ormonitored for positioning sensing. The relative positions of theopposing periodic grating teeth 2316 and 2326 on the two opposinggrating facets 2312 and 2322 can be changed due to motion of the mirrorplatform 2310 relative to the side grating top plate 2321 to causechanges in the capacitance of this capacitor. With the position of theside grating top plate 2322 being fixed in position, as the mirrorplatform 2310 changes its position due to the movement of the conductorcoil 120 engaged to the flexure actuator 110 (FIG. 1), the actualcapacitance of this capacitor can be measured and monitored to determinethe relative position of the mirror platform 2310 to the side gratingtop late 2321 along the grating direction.

In the example shown in FIGS. 23A, 23B and 23C, each of the opposinggrating facets 2312 and 2322 is shown to have a straight or flat baseprofile on which the periodic grating teeth 2316 or 2326 is formed. Insome implementations, each of the opposing grating facets 2312 and 2322may be configured to have a curved base profile to allow for motion ofthe grating facet 2312 with respect to the grating facet 2322 withoutcontacting each other during the motion.

The period of the grating teeth 2316 and 2326 can be in variousconfigurations. For example, the period of the grating teeth 2316 and2326 may be set to approximately equal to a slightly greater than thelargest displacement between the opposing grating facets 2312 and 2322caused by the motion of the mirror platform 2310. The grating period mayalso be made much greater than the displacement but this may lead aweaker output signal and thus the signal to noise ratio of the outputsignal may be reduced. For another example, the period of the gratingteeth 2316 and 2326 may be set to be much smaller than the displacementbetween the opposing grating facets 2312 and 2322 caused by the motionof the mirror platform 2310 so that the displacement covers multiplegrating periods. This configuration can be used to increase themagnitude of the signal and may improve the signal to noise ratio. Theoutput electronics can be designed to process the multiple cycles of theoutput signal during one swing of the mirror platform 2310.

More specifically, FIG. 23B shows a position where a grating tooth 2316on the mirror platform 2310 aligns with another grating tooth 2326 onthe side grating top plate 2322 to have a stronger coupling between thetwo grating facets 2312 and 2322 than other positions such as theposition shown in FIG. 23C where a grating tooth 2316 on the mirrorplatform 2310 aligns with a position between two adjacent grating teeth2326 on the side grating top plate 2322. A grating capacitive sensorcircuit is coupled to the two grating facets 2312 and 2322 to supply adesired electrical bias and to measure the capacitance to provide thefeedback control to the flexure actuator control.

The above described flexure actuator designs provide precision beamposition control and can be combined with the feedback control asdescribed in the examples of scanning beam systems in FIGS. 8A, 8B and8C to allow for improved beam positioning accuracy on the screen forhigh quality display systems and other applications. In someimplementations of the above described flexure actuator designs, fastresponses of the actuators can be achieved with reduced jitter.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of an invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments of the invention. Certain features that are described inthis patent document in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or a variation of a subcombination.

Only a few implementations are disclosed. Variations and enhancements ofthe disclosed implementations and other implementations can be madebased on what is described and illustrated in this document.

1. An actuator device, comprising: a support base; a first flexureincluding a first flexure base that is fixed to the support base andfirst flexure extensions that flex with respect to the fixed firstflexure base and the support base; a second flexure including a secondflexure base that is fixed to the support base and one or more secondflexure extensions that flex with respect to the fixed second flexurebase and the support base, the second flexure positioned and oriented tohave the first and second flexure extensions to cross; an actuatorengaged to distal ends of the first and second flexure extensions torotate around a single rotation axis as the first and second flexureextensions deform when the actuator is actuated to rotate, the actuatorbeing electrically coupled to the first flexure extension to receive anelectrical actuator drive signal through the first flexure extension tocause the actuator to rotate and to maintain at a position; a mirrorengaged to the actuator to move with the actuator and stay with theactuator; a conductive sensing plate fixed to the mirror or theactuator; a capacitor sensing device fixed in position relative to thesupport base and including two electrically conductive plates separatedfrom each other to form a gap into which the conductive sensing plate ispartially inserted; a third flexure comprising a third flexure base thatis fixed to the support base and a third flexure extension connected tothe third flexure base at one end and connected to the conductivesensing plate on the other end, the third flexure forming anelectrically conductive path that is electrically isolated from thefirst flexure and the electrical actuator drive signal therein; aposition sensing circuit coupled to the third flexure to apply anelectrical sensor signal which is conducted to the conductive sensingplate, the position sensing circuit including a processing circuit thatreceives first and second electrical signals from the electricallyconductive plates and produces a position signal from the received firstand second electrical signals indicating a relative position of theconductive sensing plate relative one of the electrically conductiveplates; and a servo control circuit coupled to the position sensingcircuit and the actuator, the servo control circuit operable to producea servo control signal based on the position signal and operable tocontrol the actuator based on the position signal.
 2. The device as inclaim 1, wherein: the actuator includes a conductor coil engaged todistal ends of the first and second flexure extensions to rotate aroundthe single rotation axis as the first and second flexure extensionsdeform when an electrical current in the conductor coilelectromagnetically interacts with a magnetic field present at theconductor coil.
 3. The device as in claim 2, wherein: the support baseincludes a magnetic module that produces the magnetic field at theconductor coil.
 4. The device as in claim 2, comprising: a magnet modulefixed in location relative to the support base to produce the magneticfield at the conductor coil to electromagnetically cause the conductorcoil to rotate around the single rotation axis in response to theelectrical current in the conductor coil.
 5. The device as in claim 4,wherein: the magnet module includes a Halbach magnet array that includespermanent magnets and a groove embedded in the permanent magnets toproduce a high magnetic flux density, and one side of the conductor coilis placed inside the groove.
 6. The device as in claim 4, wherein: themagnet module includes two Halbach magnet arrays that are symmetricallylocated at two opposite sides of the conductor coil.
 7. The device as inclaim 2, wherein: the first and second flexures are electricallyconductive and are electrically connected to the conductor coil tosupply the electrical current to the conductor coil.
 8. The device as inclaim 1, wherein: the support base includes a first protruded extensionand a second protruded extension that are located at opposite sides ofthe actuator, the first protruded extension is spaced from a first sidesurface of the actuator and the second protruded extension is spacedfrom a second side surface of the actuator, and wherein the deviceincludes a first damper pad located between and in contact with thefirst protruded extension and the first side surface to dampen a motionof the actuator relative to the support base, and a second damper padlocated between and in contact with the second protruded extension andthe second side surface to dampen the motion of the actuator relative tothe support base.
 9. The device as in claim 1, comprising: a damper padlocated between and in contact with the support base and a surface ofthe actuator to dampen a motion of the actuator relative to the supportbase.
 10. The device as in claim 1, comprising: a mirror engaged to theactuator to rotate with the actuator around the single rotation axis andto redirect light incident to the mirror as the actuator rotates. 11.The device as in claim 1, wherein: the first flexure extensions arespaced along a direction parallel to the single rotation axis.
 12. Thedevice as in claim 11, wherein: the distal ends of the first flexureextensions that are engaged to the actuator are located above the secondflexure base; and the distal ends of the second flexure extensions thatare engaged to the actuator are located above the first flexure base.13. A method for operating an actuator, comprising: engaging an actuatorto a support base by first and second flexures fixed to the supportbase, wherein the first flexure includes a first flexure base that isfixed to the support base and first flexure extensions that flex withrespect to the fixed first flexure base and the support base, and thesecond flexure includes a second flexure base that is fixed to thesupport base and one or more second flexure extensions that flex withrespect to the fixed second flexure base and the support base, thesecond flexure positioned and oriented to have the first and secondflexure extensions to cross, and wherein the actuator is engaged todistal ends of the first and second flexure extensions to rotate arounda single rotation axis as the first and second flexure extensions deformwhen the actuator is actuated to rotate; electrically coupling theactuator being to the first flexure extension to receive an electricalactuator drive signal through the first flexure extension to cause theactuator to rotate and to maintain at a position; providing a conductivesensing plate that is fixed in position relative to the actuator and tomove with the actuator; providing a capacitor sensing device, that isfixed in position relative to the support base and includes twoelectrically conductive plates separated from each other to form a gap,to insert part of the conductive sensing plate into the gap; using athird flexure, that includes a third flexure base that is fixed to thesupport base and a third flexure extension connected to the thirdflexure base at one end and connected to the conductive sensing plate onthe other end, to form an electrically conductive path that iselectrically isolated from the first flexure and the electrical actuatordrive signal therein; applying an electrical sensor signal which isconducted to the conductive sensing plate; using first and secondelectrical signals from the electrically conductive plates to produce aposition signal indicating a relative position of the conductive sensingplate relative one of the electrically conductive plates; and operatinga servo control circuit coupled to the position sensing circuit and theactuator to produce a servo control signal based on the position signaland to control the actuator based on the position signal.
 14. The methodas in claim 13, comprising: engaging a mirror to the actuator to directlight reflected off the mirror; and controlling the actuator to controla direction of the light reflected off the mirror.
 15. A display device,comprising: a light source to produce one or more laser beams that aremodulated to carry images to be displayed; and a beam scanning modulethat scans the one or more laser beams along two different directions ona screen surface to display the images and includes a first scanner toscan the one or more laser beams along a first direction and a secondscanner to scan the one or more laser beams along a second, differentdirection, wherein the first scanner comprises a mirror and a flexureactuator device that engages the mirror to rotate the mirror forscanning the one or more laser beams along the first direction, andwherein the flexure actuator device includes: a support base; a firstflexure including a first flexure base that is fixed to the support baseand first flexure extensions that flex with respect to the fixed firstflexure base and the support base; a second flexure including a secondflexure base that is fixed to the support base and one or more secondflexure extensions that flex with respect to the fixed second flexurebase and the support base, the second flexure positioned and oriented tohave the first and second flexure extensions to cross; an actuatorengaged to distal ends of the first and second flexure extensions torotate around a single rotation axis as the first and second flexureextensions deform when the actuator is actuated to rotate, the actuatorbeing electrically coupled to the first flexure extension to receive anelectrical actuator drive signal through the first flexure extension tocause the actuator to rotate and to maintain at a position; a mirrorengaged to the actuator to move with the actuator and stay with theactuator; a conductive sensing plate fixed to the mirror or theactuator; a capacitor sensing device fixed in position relative to thesupport base and including two electrically conductive plates separatedfrom each other to form a gap into which the conductive sensing plate ispartially inserted; a third flexure including a third flexure base thatis fixed to the support base and a third flexure extension connected tothe third flexure base at one end and connected to the conductivesensing plate on the other end, the third flexure forming anelectrically conductive path that is electrically isolated from thefirst flexure and the electrical actuator drive signal therein; aposition sensing circuit coupled to the third flexure to apply anelectrical sensor signal which is conducted to the conductive sensingplate, the position sensing circuit including a processing circuit thatreceives first and second electrical signals from the electricallyconductive plates and produces a position signal from the received firstand second electrical signals indicating a relative position of theconductive sensing plate relative one of the electrically conductiveplates; and a servo control circuit coupled to the position sensingcircuit and the actuator, the servo control circuit operable to producea servo control signal based on the position signal and operable tocontrol the actuator based on the position signal.
 16. The device as inclaim 15, wherein the screen include light-emitting materials thatabsorb light in the one or more laser beams from the light source toemit light which produces the images.
 17. An actuator device,comprising: a support base; a first flexure including a first flexurebase that is fixed to the support base and first flexure extensions thatflex with respect to the fixed first flexure base and the support base;a second flexure including a second flexure base that is fixed to thesupport base and one or more second flexure extensions that flex withrespect to the fixed second flexure base and the support base, thesecond flexure positioned and oriented to have the first and secondflexure extensions to cross; an actuator engaged to distal ends of thefirst and second flexure extensions to rotate around a single rotationaxis as the first and second flexure extensions deform when the actuatoris actuated to rotate, the actuator being electrically coupled to thefirst flexure extension to receive an electrical actuator drive signalthrough the first flexure extension to cause the actuator to rotate andto maintain at a position; a platform fixed to the actuator and to movewith the actuator, the platform including a first side grating facetthat has electrically conductive first grating teeth that areelectrically connected to one another; a side grating module fixed tothe support base and separated from the platform and the actuator sothat platform and the actuator move relative to the side grating module,the side grating module includes a second side grating facet that haselectrically conductive second grating teeth that are electricallyconnected to one another and positioned adjacent to the first gratingteeth and separated from the first grating teeth by a gap; a positionsensing circuit coupled to the first grating teeth and the secondgrating teeth to apply an electrical sensor signal, the position sensingcircuit including a processing circuit that receives first and secondelectrical signals from the first and second grating teeth,respectively, and produces a position signal from the received first andsecond electrical signals indicating a relative position of the platformrelative to the side grating module; and a servo control circuit coupledto the position sensing circuit and the actuator, the servo controlcircuit operable to produce a servo control signal based on the positionsignal and operable to control the actuator based on the positionsignal.
 18. The device as in claim 17, wherein: the actuator includes aconductor coil engaged to distal ends of the first and second flexureextensions to rotate around the single rotation axis as the first andsecond flexure extensions deform when an electrical current in theconductor coil electromagnetically interacts with a magnetic fieldpresent at the conductor coil.
 19. The device as in claim 18, wherein:the support base includes a magnetic module that produces the magneticfield at the conductor coil.
 20. The device as in claim 18, comprising:a magnet module fixed in location relative to the support base toproduce the magnetic field at the conductor coil to electromagneticallycause the conductor coil to rotate around the single rotation axis inresponse to the electrical current in the conductor coil.
 21. The deviceas in claim 18, wherein: the first and second flexures are electricallyconductive and are electrically connected to the conductor coil tosupply the electrical current to the conductor coil.
 22. The device asin claim 17, wherein: the support base includes a first protrudedextension and a second protruded extension that are located at oppositesides of the actuator, the first protruded extension is spaced from afirst side surface of the actuator and the second protruded extension isspaced from a second side surface of the actuator, and wherein thedevice includes a first damper pad located between and in contact withthe first protruded extension and the first side surface to dampen amotion of the actuator relative to the support base, and a second damperpad located between and in contact with the second protruded extensionand the second side surface to dampen the motion of the actuatorrelative to the support base.
 23. The device as in claim 17, comprising:a damper pad located between and in contact with the support base and asurface of the actuator to dampen a motion of the actuator relative tothe support base.